Field of the Invention
The present embodiments herein relate to the field of storage tanks for fluid cryogens. In particular, the present embodiments herein relate to the field of cryogens such as, cryogenic fluid hydrogen stored in composite pressure vessels.
Discussion of the Related Art
Cryogenic fluids, such as, hydrogen is known to be a desirable vehicular fuel for aerospace, marine, and terrestrial applications. Motivation comes from the fact that in many aerospace and unmanned aerial vehicle applications, the benefits of hydrogen outweigh the challenges. For example, beneficial aspects of hydrogen include the highest specific energy (J/kg) of any chemical fuel that is 2.8 times higher than conventional kerosene, rapid spill dispersion, ultra-green emissions, ease of production from water, and highly reliable and efficient solid state fuel cell power systems. However, a primary challenge with utilizing hydrogen fuel is storage.
In order to take advantage of the high specific energy of hydrogen, the associated tanks are preferably light weight—ideally being just a small fraction of the weight of the stored hydrogen (and preferably on the order of 10% to 25% of overall system weight). However, typical tanks for storing compressed gaseous hydrogen have a weight of about 10 to 20 times that of the hydrogen stored, and are not likely practical for high-altitude, long-duration aircraft. Moreover, liquid hydrogen powered long-endurance vehicles typically require tanks with sufficient insulation to prevent complete boil-off due to ambient heat for less than one to two weeks. An anticipated capacity of an individual tank might range from <1 to 2000 pounds of fluid hydrogen, depending on the configuration and size of the airplane.
The method of insulating a tank must deal with several types of heat transfer: conduction through solids, conduction and convection of fluid, and radiation. Most methods of effecting high-performance insulation rely on a vacuum to nearly eliminate the conduction and convection gas heat transfer. Solid conduction is conventionally reduced by having the insulated tanks supported in the vacuum by structural supports of high-strength to conductivity ratio (e.g., stainless steel, glass fiber, or Dacron fiber). Nonetheless, such systems have inherent problems that include cracking of the tank insulation due to mismatched coefficients of thermal expansion and pressure fluctuation induced swelling and a need for configured vacuum jackets to be continually purged of residual gas via vacuum pumping due to excessive hydrogen permeation through the tank wall. In addition, a weight intensive heat exchanger and electric heater are often required to heat the fuel to prevent condensation of air or water outside to piping outside the tank.
In spite of these challenges, use of hydrogen for fueling such vehicles has been demonstrated as an efficient and environmentally friendly solution. The most straightforward approach entails directly compressing the hydrogen and storing the room temperature gas in conventional high pressure vessels but the fuel density is not competitive from a capacity and performance standpoint with cryogenic hydrogen. Liquid hydrogen is typically stored in spherical tank structures, however, there are difficulties in manufacturing and incorporating tank structures (e.g., spherical tank structures) into existing Unmanned Aerial Systems (UAS) systems.
Thus, there is a need in the industry for a novel design and construction of a robust and light-weight, cryogenic compatible fuel tank with respect to hydrogen fuel storage to power vehicles, such as, but not limited to, automotive, aerospace and unmanned aerial vehicle systems. The embodiments herein address such a need by combining manufacturing systems with an inherent property of hydrogen to substantially reduce the hardware associated with a fuel tank, the end result of which is a novel effectively insulation-free, competitive, cost effective, cryogenic hydrogen fuel tank with inherent safety features for vehicles.